The emergence of Voice-over-Internet Protocol (VoIP) and other data packet-based multimedia calling services has resulted in the co-existence of two different addressing schemes: the conventional telephone numbering scheme in accordance with the Internet Engineering Task Force (IETF) E.164 standard for user equipment on the public switched telephone network (PSTN); and the Internet Protocol (IP) addressing scheme in accordance with the IPv4 or IPv6 standards for user equipment on IP packet-based networks. Telephone number mapping processes often are used to unify these disparate addressing schemes, the most prominent of which is the International Telecommunication Union (ITU) Telephone Number Mapping (ENUM) specification. This specification makes use of domain name server (DNS)-type records to translate E.164 telephone numbers into a corresponding Uniform Resource Identifier (URI), which then may be used to identify a corresponding IP address for establishing a communications session, or multimedia call, between subscribers.
The use of the same reference symbols in different drawings indicates similar or identical items.